With reference to FIGS. 6a, 6b and 6c, which illustrate an electric centrifugal fan of a type known in prior art, fans of this type comprise a casing “a” that houses an impeller “b” represented schematically in FIG. 6b and connected to an electric motor “c”. The casing “a” has an opening (not illustrated) in the side of it to draw air into it in a direction parallel with the axis of rotation of the impeller “b” and a discharge opening “d” through which the impeller “b” blows the air out in a direction “e” tangential to the impeller “b” itself. The discharge opening “d”, is delimited by four lateral edges which define a plane “f” perpendicular to the air flowing out and parallel with the air flowing in. More specifically, a first edge “g” is substantially parallel with the axis of rotation “h” of the impeller “b”, is located in the vicinity of the impeller “b” and belongs to a first wall “i” parallel with the plane “f” defined by the discharge opening. A second edge “l”, parallel with and opposite the first, is spaced from the impeller “b” and belongs to a second wall “m” substantially perpendicular to the plane “f” defined by the discharge opening “d”. Two lateral edges “n”, each joining the first edge “g” to the second edge “l”, belong to opposite walls “o” perpendicular to the axis of rotation “h” of the impeller “b”. Disadvantageously, all the edges “g, l, n” have sharp edges. Also, the casing “a” is closed by a curved wall “p” which joins the first wall “i” to the second wall “m” and, together with the impeller “b”, delimits a duct “q” that diverges towards the discharge opening “d”.
In the modern automotive industry, in particular in the field of luxury car production, driving comfort has reached very high levels in terms of both the car's dynamic behaviour and noise. Having attained extremely high levels of soundproofing against outside noise, designers are now concentrating their attention on noise inside the cabin or in parts of the car near the cabin such as, for example, the noise made by the fans of the car's air conditioning and/or heating system.
In this regard, the Applicant has found that fans of the type described above can be improved in several ways, especially as regards the noise made by the air flowing against the sharp edges of the fan. This noise disturbs the driver and passengers.